Method of tempering glass articles



Patented July 21, 1942 NT OF FlCE- METHOD E- TEMIPEBJNG GLASS ARTICLESDonald W. Mueller, West Hartford, Conn., as-' signor to Hartford-EmpireCompany, Hartford, Oonn., a corporation of Delaware No Drawing.

Application Februar 1, 1940,- Serial No. 316,805

8 Claims. '(01. 4 9) This invention relates to the tempering of glassarticles and more particularly to-the tempering of hollow glassarticles, such as bottles and jars. Y a

A glass article is tempered by cooling it abruptly through a suitabletemperature range to cause therein permanent stresses in the form ofcompression of its surface layers and tension of its inner layers. Thelower limit of this tempering temperature range is that temperaturebelow which further abrupt cooling of the, article will not createanypermanent stresses therein but onlytransient stresses which willdisappear on or before completion of cooling of the article to roomtemperature. This lower tempering limit is somewhat below the strainpoint (log. viscosity=l 3.4 the latter being that. point below whichmoderate cooling, as in annealing operations,- will not create anypermanent stresses in the glass. The upper limit of this temperingphysical features.

range is practically that temperature at or very near the softeningpoint of the glass article at which the necessary handling ormanipulation of the glass article to permit the required tem-' peringoperation can be effected without objectionable deformation of thearticle.

The tempering range and the upper and lower limits thereof vary with thecomposition and nature of different glassarticles." Ofcourse, part orall of the glass of an articl may be heated to a temperature higher thanits softening point before abrupt cooling thereof is commenced.

The degree of temper per unit of thickness of a -piece of a temperedglass article may be termed its temperity. The product of temperitytimes thickness is a measure of the increase in strength imparted to thepiece of the glass article by the tempering operation.

. The teaching of the prior art is that the a higher in its temperingrange at which abrupt cooling of an article is commenced and" thegreater the cooling rate atwhich the temperature of the article beingtempered is lowered through that range, -the greater will be thetemperity of the tempered article. Proposals for tempering article downto and through thelower limit of its tempering range. So far as Iam'aware, no such proposal has resulted in a satisfactory, commerciallyused, method of tempering hollow glass articles, such as bottlesandjars, as they are produced rapidly by known commercial methods andmachinery.

' A general object of the present invention is to obviate or curedefects which I have discovered in such prior proposals and which willnow be pointed out. I

Hollow glass articles of commerce are of an almost, infinite number ofspecifically different shapes. Each such article has walls which aredifferent at a number of places in thickness; I curvature, angularity,direction in respect to the central axis of the article, diameter ortransverse area, or some other physical feature. Even 'articles of thesame kind as produced in sucsurface and on the outer surface of a hollowglass .article that is being tempered so that all portions of all wallsof that article will be'cooled at exactly the difl'ering rates requiredto provide the desired primary or temperity permanent stresses in theform of compression of the surface layers and tension of theintermediate layers of glass of eachportion of each wall of the articlewithout also causing undesirable secondary, nontemperity permanentstresses in the form of bending moments and/or unsuitably locatedtensionon glass of the article. These secondary stresses, if sufiiciently greatat any place, may actually eigceed the primaryortemperity stresses,which have no bending moment. They may create a condition of tension at,the surface of one or more portions of the tempered article and thusgreatly weaken the article at such point or points. I have classifiedbothy-the primary and. secondary stresses as permaneii as both willpersist in a finally cooled article while that inevitable secondarypermanent stresses in hollow glass articles that have been temperedaccord-.

'article remains intact.

The prior proposals fortempering glass articles to which I have referredfail to take into consideration the presence of 'these' undesirable buting to such proposals or topoint out any way of diminishing or dealingwith such secondary ressesv 91 the injurious effects thereof. a.

Many of such articles have v that is employed tends to create in thetempered article.

A further object of the invention is to effect a'substantial reductionin the time required for tempering of a hollow glass article from thatrequired by prior proposals.

The presentinvention is based in part on the discovery of the source ofthe hereinbefore described defects in the prior proposals for temperinghollow glass articles, such as bottles or jars, and in part on aconception and development of a practical way of remedying such defects.I

have discovered thatthe harmful nontemperity secondary stresses createdby the abrupt cooling of an article'ofhollow glassware to create primaryor temperity stresses therein will vary. when any known cooling means oragency is employed directly with the length of the tempering rangethrough which suchabrupt cooling is effected. To carry out the presentinvention, based in part on this discovery, I propose,- as thepreferredmethod of tempering a particular hollow glass article to start theabrupt cooling thereof at a point in its tempering range immediately ornot much above that at which the application of cooling medium to thearticle to cool itat the rate required to provide the temperity desired.

would cause breakage or rupture of the article.

According to the present invention, there is for each particular type ofhollow glass article a combination-of a most suitable relatively lowstarting point of abrupt cooling in the tempering temperature range ofthe article and a most suitable cooling rate for the production ofapartempering temperature range for a particular article, usually beingrelativelynear to the midway point of that range, and that any higherstarting point within the purview of the present invention for obtainingthe same or approximately the same temperityby the use of a lower.cooling rate is still substantially below that at which cooling shouldbe started according to asfollows: Chemical composition v 0 1 PercentSilica (SiOz) (by difference) 73.37 Iron and alumina. (R201) 1.23

40 Calcium oxide (CaO) 5.08} 878 Magnesia (MgO) 3.70 f Barium oxide(Ba0)- .33 7 Sodium oxide (NazOL 15.34} 95 Potassium oxide (KaO).. .61 QBoric oxide (B203) .34

ticular temperity in the article with a minimum particular articleand-thereafter used for the tempering of othersimilar articles. Thelocaprior proposals, generally being within a range of approximately F.upward from the most suitable starting point.

Each glass article may be chilled abruptly from a relatively lowstarting point in its tempering temperature range to or below the strainpoint of the glass of the article, after which more moderate cooling ofthe article maybe effected to bring itto room or handling temperature.The change from abrupt chilling to more moderate' cooling of the articleafter'it has passed its strain point may. be at its lower tempering;limit or at a still lower temperature, as determined for a particulararticle by individual preference, convenience or service conditions. Ofcourse, no further permanent stresses will be created in the glass bythe cooling thereof, whether abrupt or moderate, after the glass isbelow its lower tempering limit.

' The following'explanation of operations which I have performed onhollow glass articles of a particular type, i. e., stubby beer bottles,will aid in afiording anunderstanding of the invention and of thepractice thereof. These stubby bottles were made from glass havingcharacteristics 1 Specific gravity (25.5, C./25.5 C.),.2.4877. Softeningtemperature, 1288* F. Strain point (log'. viscosity=13.4), 894' F. Anumber of these bottles-were brought to a uniform temperature throughoutat 1115 F.'

' They were then cooled abruptly from that tem tion of themost'suitable' starting point in "the tempering temperature rangeinvolved and the most suitable cooling rate will vary according to thetemperity desired a'nd.with the shape andother physical features-and thecomposition of g the; article.

It is, however, within the purview of the inventempering scale from themost suitable starting point for a given hollowarticle, and to usecooling rates correspondingly lower than the most suitable cooling ratein order to provide the same or approximately the. same: temperity ofsuch ,article. Such departures from the, most suitable and preferredstarting point. and cooling rate will be attended by increases in theundesirable secondary permanent stresses in the articles and operationsand thus tend to deprive the user of the maximum possibleadvahtages ofthe inven- "tion. It is to be noted, moreover, that, in each instance,the most suitable starting point in'order to obtain adequate temperityis far down in the shape, mass, etc. The coolant employed was air in theperiods of time required for the .cooling. 70 under a'pressure orapproximately 30 lb. per sip perature to a temperature just below thestrain point. The cooling means employed was similar to that whichis.disclosed'in the application of Thomas D. Green, Serial No. 306,085,filed November 25,- 1939, which includes'a nozzle'for, applying jets ofair to the internal surface of the bottle anda cooperative cooling airappli-.

-cator for applying jets of airto the external surface of the bottletogether with a means for efiectingfa relative rotation between thebottle and the jets of cooling air impinging on the surfacesthereof, theaxisof rotation being that of the bottle.: This cooling means alsoincludes provisions intended and utilized as fully as possible toapportionthecoolant to different portions of the bottles in accordancewith the differing physical features 0t such portions, such as 2,290,7633 1115 F. down to fie strain point. The bottles of temperature having anupper limit far below were well'tempered, having" an average temperitythe softening points of the articles-involved and of approximately 1100millimicrons per centia lower limit at least far enough above the strainmeter squared (being the,m'aximum retardation point of any such articleto permit tempering per unit light path per'unit thickness of glass). 5of the article by the use of the cooling mecha- They exhibited thedesired primary stresses in nism available for that purpose. This lowerthe form of compression of surface layers and limit is approximately 150F. above the strain tension of internal-layers of the glass throughout"point for the stubby beer bottles and generally all portions of eachbottle. The undesirable secsimilar articles but may be less forcertainpar- ,ondary stresses were. noted'but were not of sufm ticular types ofarticles.

ficient consequence to render the tempering op- Variations incapabilities and efliciencies of eration or the tempered bottlescommercially unavailable cooling mechanisms or cooling mediasatisfactory. employed for tempering may affect the locations I thentempered similar' bottles to the same of the most suitable startingpoints for temperdegree of tempenwith the same mechanism and as ingdifferent hollow glass articles to the temperaccording to the sameprocedure except that the itie's desired, and also the extent of upwardbottles were brought to thermal uniformity at a ranges from suchstarting points of permissible temperature as near the beginning ofsoftening locations of starting points from which such aras risk ofdeformation of such bottles on hanticles may be cooled at lower rates tothe same dling would permit and cooling was efiected at I temperitieswithout prohibitive" secondary a rate that had been reduced inproportion to stresses.

the increase of starting temperature. The time When temperatures ofglass articles are given required to bring' the temperature'of thesebot-' herein or in the appended claims, they are to tles down to thestrain pointwas of course greatbe understood as mean or averagetemperatures .ly-increased and the tempered bottles had the if thearticles in question have different temundesirable secondary stresses ofsuch magniperatures'at dlfierent parts. Similarly, cooling tude andcharacter as greatly to impair the rates given are mean or average ratesunless strength of the bottles. Otherwise stated if difierent portionsof the ar- 1 then tempered other similar bottles by the ticles involvedare subjected to different cooling use of the same mechanism andaccording to 3 influences orcooled at different rates.

the same procedure in order to ascertain a per-0 The invention has beendescribed herein with missible range of locations of the starting pointparticular reference to its use in tempering holin the temperingtemperature range 'in order low glass articles, such as bottles andjars. It

to provide substantially the same temperity, i. e., may however beusefully employed in tempering approximately 1100 millimicrons percentimeter all glass articles, including fiat glass, which are squared,without prohibitive secondary stresses. cooled during tempering in suchmanner and by For the particular bottles in question, using the suchmeans as to cause undesirable secondary cooling apparatus referred to, Ifound that satisstresses therein. I

factory tempered bottles of the temperity just What I claim is: e

mentionech were obtained when abrupt cooling 40 1. The method ofprocessing a hollow glass thereof was started withina range extendingarticle to temper it to a particular temperity upwardly from ll15-F. toapproximately 1185" F. and at the same time to minimize non-temperityTheformer was the lowest starting point at or secondary stresses thereinwhich consists in which the cooling rate required to provide. thepredetermining the factors of said temperity in temperity desired couldbe applied by the use of terms of the lowest possible safe startingtemthe cooling mechanism of the'afor'es'aid Green perature and the rateof abstraction of heat application without undue risk of breakage of Ifrom the article required to temper it to said the bottles during thetempering operation. The temperity without causing it to break, bringinglatter was the highest point from which the botthe article to or closelyabove said starting point,

tles could be cooled down abruptly by the use,of rm and then cooling itrapidly to a temperature bethe same cooling means to cool the bottlesatlow its strain point by applyingto the surfaces the lower rate requiredto produce the same temof said article jets of cooling gaseous mediumperity without causingundesirable secondary regulated as to coolingefiect on different porstresses of sufiiciently great magnitude orextent 'tions of said article to provide said rate of abto constitute asubstantial source of Weakness in straction of heat with a minimum ofdisproporeach such bottle. tionate cooling of said different portions ofthe The temperity referred to, i. e., approximately article. 1100niillimicrons per centimeter squared, is 2. The method of processingglass articles to adequately high for most commercial requirv p Prmanent temperi ses and to 'ments relating to the strength and toughness6U minimize non-temperityor secondary stresses of most hollow.articles.Indeed, much lower therein which consists in bringing the glass oftemperities woul'd ordinarily be satisfactory. As each such article to atemperature not greatly aforesaid, the temperity of a given article thatin excess of the midway point of its tempering to be obtained willcontrol the identity of the temperature range, and rapidly cooling theglass combination of the most suitable starting point of the a'rticie tothe lower limit of its said temand the cooling rate that should be usedto propering temperature range at the cooling rate vide that temperity,making use,v of course, of required to provide the desired temperity.inthe the most satisfactoryavailable cooling mechaarticle. v v nism. Ingeneral, both the most suitable start- 3. The method of tempering abottle, jar

ing point and its cooperative cooling rate will be other hollow glassarticle, the walls of .which higher the higher the temperity desiredand. are different for different parts of the article lower if a lowertemperity will sufilce. For a in thickness, curvature, directioninrespect to Substantial range O temperities f t ypes the central axis ofthe article or .diameter, to

of hollow glass articles of commerce, the most a predetermined temperitywithout creating proitable starting points all be within a [rangehibitive non-temperity or secondary stresses therein which consists inbringing the article to a starting temperature substantially below itssoftening point and substantially above but not exceeding. 291 F. aboveits strain'point, and

rapidly cooling the article from said starting 6 temperature to atemperature below said strain point by applying to said article acooling infiuence regulated to provide the cooling rate required toproduce..said temperity andto minimize disproportionate cooling ofdiflerent porl0 tions of -the article.

4 The method of tempering hollow glass articles the glass of which has:a softening point in the neighborhood of '1288" F. and a strain point'(log. viscosity =13.4) in the neighborhood 15 idly cooling safd articlefrom said starting tem- 20 perature to: a temperature below the strainpoint of the glass of said article. I 4

5. The method of tempering hollow glass articles, the glass of, whichhas a,-softening point in the neighborhood of 1288 F. and a strain- 5point: (log. viscosity=l3.4 in the neighborhood of 894 E, whichcomprises bringing each such article to a starting temperature locatedwithin a range extending upwardly from approximately 1115 F. toapproximately 1185 Fr, and rapidly 30 cooling said article from saidstarting temperature to a temperature below the strain point of theglass of said article at the highest available cooling rate said articlewill endure without 6. The method oi tempering hollow glassanticles, theglass of which has a. softening point mule neighborhood or 1288*" r. anda strain point (log. viscosity=13.4) in the neighborhood of 894 F.=, tosubstantially the same temperity which comprises bringing each sucharticle to a starting temperature located within a range extendingupwardly from approximately 1115' F. to approximately 1185? F., andrapidly cooling said article from said starting temperature to atemperature below the strain point of the glass of saidarticle at arelatively high rate when the starting temperature is approximately11'15 F. and at a proportionately reduced rate when the startingtemperature is higher in said ans V 7. The method of tempering hollowglass articles, the glass of which has a softening pointlathe-neighborhood 01' 1288 F. and a strain point (log. viscosity=l3.4)in the neighborhood oi 894 E, which comprises bringing each such articleto a starting temperature below an upper limit of approximately 1185"F., and rapidly cooling said'article from said starting temperature to atemperatu'rebelow the strain point of the glass of said article.

8. The method of tempering hollow glass articles, the glass of which hasa softening point in the neighborhood of '1288 F. and a strain point.(log'. viscosity=l3.4) in the neighborhood of 894 E, whichcomprisesbringing each such article to a starting temperature not inexcess to! approximately 1185 F., and rapidly cooling saidaarticle fromsaid starting temperature to a temperature below the strain point of theglass I of said, article at the highest available cooling breaking atits said starting temperature. ,35

rate said article will endure without breaking at its said startingtemperature. r v

DONAIDW.MUELIER.

